1. Field of the Invention
This invention relates in general to calibrating scanners, and more particularly to a process and system for effectively and efficiently calibrating a scanner.
2. Description of the Related Art
A problem prevalent in conventional scanners involves the process of maintaining or calibrating the scanner to regularly obtain optimal efficiency. The calibration process is used to correct for offset errors and gain errors in the sensor's signal. Offset and gain errors can be caused by the characteristics of individual components responsible for converting the light reflected from the image into electronic image data. These errors may result from nonuniformities in the characteristics of the illumination and sensing components in the scanner, as well as from time varying drifts of such characteristics. For example, a charged coupled device (CCD) sensor may have inherent offset and gain characteristics unique to itself or a scanner may contribute to offset and gain errors due to the present operating conditions. The operating conditions could include the operational temperatures, lamp color and intensity, system noise, exposure balance, current draw, etc.
If offset errors or gain errors are not adequately addressed (i.e. the signal being processed is not adjusted to counteract the offset or gain errors) the processing of the signal will not be accurate which, in an image processing system, can cause the generated picture or image to have a lower quality.
To address these problems, typical image processing systems or image scanning systems perform calibrations of the imaging system at intervals. Often, the calibration is performed at power-up but, in some cases, calibration is performed at fixed intervals, sometimes as frequently as each scan. Each calibration will typically take longer than the time required to scan a document. Consequently, a user typically wastes a lot of time waiting for a scanner to calibrate before a document can be scanned.
The time required to calibrate a scanner is related to the time it takes for a scanner to obtain the reference reflectance values of a calibration strip. For example, during the calibration of digital scanners, an imaging capture system is positioned to allow a sensor array to view a strip of calibration information and/or patterns located on or near the platen. It is important that an accurate value of the reflectance of this calibration strip be known to the digital scanner to achieve an absolute reflectance calibration and generate accurate correction values for subsequent document reading operations.
In summary, conventional application software for a scanner will typically calibrate a scanner only after a specific condition. A condition could include a scanner being powered-on, the user requesting a calibration, a predetermined number of scans being completed, and a prescan setting. With any of these conditions, no portion of an earlier calibration or scan can be used to expedite the scanning process. Consequently, the user must wait for a calibration of a scanner before their scan will be performed.